Improve examples and documentation

examples/phalcon-mysql.yml

@@ -30,6 +30,8 @@ jobs:
       fail-fast: false
       matrix:
         php-versions: ['7.2', '7.3', '7.4']
+      # For phalcon 3.x, use
+      # php-versions: ['7.0', '7.1', '7.2', '7.3']
     steps:
       - name: Checkout
         uses: actions/checkout@v1
@@ -46,6 +48,8 @@ jobs:
         uses: actions/cache@v1
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
+          # Use composer.json for key, if composer.lock is not committed.
+          # key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
           restore-keys: ${{ runner.os }}-composer-
       - name: Install Composer dependencies